In gynecologic cancers such as breast cancer and endometrial cancer, the activities of the estrogen receptor and the estrogen-biosynthesizing enzyme in the tumor tissue are higher than those in the normal mammary gland tissue and the endometrial tissue, and the proliferation of these tumors have close relation to endogenous or local increase of estrogenic activity. Thus as one means for therapy of gynecologic cancers, it is put into practice to make competition against the estrogenic effect in the estrogenic target tissue, namely to administer antiestrogenic agents.
Among these antiestrogenic agents, a compound of the following formula called tamoxifen was, first, proposed (see, UK Patent No. 1,013,907). ##STR3## Tamoxifen is now widely used for treatment of breast cancer, etc. as a representative antiestrogenic agent. Thereafter, several kinds of compounds having the same characteristic as tamoxifen is chemical structure, namely three benzene rings were proposed as antiestrogenic agents (see, for example, Proc. Soc. Exp. Biol. Med., 112, 439-442 (1963), J. Med. Chem. 8, 725-726 (1965), J. Med. Chem., 22, 962-966 (1979)).
Further, several benzothiophene derivatives having an antiestrogenic activity have been known (see, Japanese Laid-Open Patent Publication No. 181081/1982, Life Sci., 26, 1453-1458, 1980). Among them, a compound of the following formula called raloxifene has a very strong antiestrogenic activity, and is now under clinical tests. ##STR4##
However, all of these antiestrogenic agents also have an estrogenic activity too strong to be neglected, simultaneously with the antiestrogenic activity, and they were yet unsatisfactory in this point.
The present inventors have intensely researched for benzothiophene derivatives having an antiestrogenic activity, and as a result have found that a series of compounds wherein a specific substituent such as a cycloalkyl group or a lower alkyl group was introduced in place of a substituted phenyl group so far known as the substituent as the 2-position of the benzothiophene nucleus have a strong antiestrogenic activity but have only a very weak estrogenic activity.